The invention relates to a picture display device comprising a colour display tube having an elongate display screen with a short axis and a long axis, which screen is provided on an inner surface, a colour selection system arranged in front of the display screen, an electron gun system arranged opposite the display screen for producing co-planar beams, and a deflection system arranged between the electron gun system and the display screen.
Conventional picture display devices of the type described above often have an electron gun system with three guns which are located in one plane. The plane in which the undeflected beams are located is parallel to the long axis of the display screen. The orthogonal deflection fields generated by the deflection system upon energization generally have such a (pincushion and barrel) configuration, viewed in planes transverse to the axis of the display tube, that the display device is self-convergent.
A problem in this type of display device in its current form is the increase in the dimension of the spot in the direction of the long axis of the display screen as the deflection in that direction increases. This problem is not new, but it will become even more manifest in future HDTV systems.